Study explains early warming of West Antarctica at end of last ice age
CORVALLIS, Ore. – West Antarctica began emerging from the last ice age about 22,000 years ago – well before other regions of Antarctica and the rest of the world, according to a team of scientists who analyzed a two-mile-long ice core, one of the deepest ever drilled in Antarctica.
Scientists say that changes in the amount of solar energy triggered the warming of West Antarctica and the subsequent release of carbon dioxide (CO2) from the Southern Ocean amplified the effect and resulted in warming on a global scale, eventually ending the ice age.
Results of the study were published this week in the journal Nature. The authors are all members of the West Antarctic Ice Sheet Divide project, which was funded by the National Science Foundation.
The study is significant because it adds to the growing body of scientific understanding about how the Earth emerges from an ice age. Edward Brook, an Oregon State University paleoclimatologist and co-author on the Nature study, said the key to this new discovery about West Antarctica resulted from analysis of the 3,405-meter ice core.
“This ice core is special because it came from a place in West Antarctica where the snowfall is very high and left an average of 20 inches of ice or more per year to study,” said Brook, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Not only did it allow us to provide more accurate dating because we can count the layers, it gave us a ton more data – and those data clearly show an earlier warming of the region than was previously thought.”
Previous studies have pointed to changes in the Earth’s orbit around the sun as the initial trigger in deglaciation during the last ice age. An increase in the intensity of summer sunlight in the northern hemisphere melted ice sheets in Canada and Europe starting at about 20,000 years ago and is believed to have triggered warming elsewhere on the globe.
It previously was thought that Antarctica started its major warming a few thousand years later, at about 18,000 years before present. However, the new study shows that at least part of Antarctica started to warm 2,000 to 4,000 years before this. The authors hypothesize that changes in the total amount of sunlight in Antarctica and melt-back of sea ice caused early warming at this coastal site – warming that is not recorded by ice cores in the interior of the continent.
“The site of the core is near the coast and it conceivably feels the coastal influence much more so than the inland sites where most of the high-elevation East Antarctic cores have been drilled,” Brook said. “As the sunlight increased, it reduced the amount of sea ice in the Southern Ocean and warmed West Antarctica. The subsequent rise of CO2 then escalated the process on a global scale.”
“What is new here is our observation that West Antarctica did not wait for a cue from the Northern Hemisphere before it began warming,” Brook said, “What hasn’t changed is that the initial warming and melting of the ice sheets triggered the release of CO2 from the oceans, which accelerated the demise of the ice age.”
Brook said the recent increase in CO2 via human causes is also warming the planet, “but much more rapidly.”